Measurement of propeller forces exciting hull vibration by use of self propelled model

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ARCH1

Measurement of Propeller Forces

Exciting Hull Vibration by Use of

Self-Propelled Model

By

Toyoji KUMAI, Tetsujir6 TOMITA, Fukuzö TASAI,

Toshirö SuHARA, Toshi IZUCHI, Hiromi HIYAMA and Shigehisa FIJKUDA

Reprinted from Reports of Research Institute for Applied Mechanics, Kyushu University

Vol. IX, No. 33, 1961

.

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y. Scheepbouwkunde

Thchnche HcgeschooJ

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Reports of Research Institute for Applied Mechanics Vol. IX, No. 33, 1961

MEASUREMENT OF PROPELLER FORCES

EXCITING HULL VIBRATION BY USE OF

SELF-PROPELLED MODEL by

Toyoji KUMAI,* Tetsujirò TOMITA,**. Fukuzö TAsAI,*** Toshirö SuHARA,**

_{Toshi Iz ucin,'}

Hiromi HIYAMA, * _{and Shigehisa FUKUDA* *}

Summary

The present report provides the experimental study on the measurements of propeller forces exciting hull vibration by use of self.propelled model.

The special considerations are given for measuring the components of the reactions of propeller shaft at the bearing, and surface forces applied at the end parts of the stern as well as those of the thrust and torque variations.

The experiments were carried out by making model ship selfpropel along about 200 m straight course in a reservoir, where manipulation, operation of the meters equipped in the ship and recording were all conducted by wireless instructions. The effects of number of blades of propeller on the vibratory

exciting forces on the ordinary stern and Weser stern are obtained by

replacing 3, 4, 5 and 6-bladed propellers for two models. The effect of screw

aperture on the vibratory propeller forces in the ordinary stern is also

obtained.

Introduction

The model experiment on the measurement of propeller exciting forces was

originated by F. M. Lewis. In the model experiment carried out on a single screw cargo ship of four bladed propellers by F. M. Lewis and A. J. Tachminji, vertical and horizontal forces on stem and the moment around the central axis of hull were measured as apparent exciting forces and then the effects of clearance of

propeller and hull or rudder on that were examined. Furthermore, removing bearing force from all exciting forces by putting propeller in the condition of behind test, surface force was evaluated [1]. Lewis' method is an indirect measurement of exciting force. On the other hand, in K. Taniguchi's experiment by self-propelled model, only bearing force has been measured by direct

measure-Professor of Kyushu University, member of the Research Institute for Applied Mechanics, Chief of Planning and Estimating Section, Hull Department, Mitsui Shipbuilding and Engineering Co. Ltd.

Assistant Professor of Kyushu University, member of the Research Institute for Applied Mechanics,

' _{Assistant of the Research Institute for Applied Mechanics.}

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2 T. KUMAL et ai.

ment, in which effects of the form of rudder on both vertical and horizontal forces at propeller boss were examined supporting the propeller axis elastically and availing this displacement [2]. Also in the recent experiment [3] of van Manen-Wereldsma, the variation of vertical and horizontal bending moment conveyed from propeller to main shaft was directly measured by putting a strain gauge close to the propeller boss of main shaft, and the effects of stern form and the number of propeller blades

upon these and the variation of thrust and torque were investigated. Again in K. Taniguchi s theory and experiment [4], pressure change caused on the bottom of

box-type model ship by the propeller revolution was evaluated on various kinds of propeller and tip clearance, where a method of estimating surface force on the bottom of a twin screw ship and a cruiser stem is shown. K. H. Pohl [5] also

carried out similar experiment on a single screw model ship, measuring the vertical pressure variation imposed on stern with respect to venous kinds of propellers.

Propeller exciting force can be generally divided into six components, i. e., vertical and horizontal forces P, P11, moments MT-, M, torque Q and thrust T.

In the present experiment, vertical and horizontal forces and moments imposed on propeller boss and thrust and torque were measured by making a model of 50,000 ton tanker (5.0 m length, 1/44 in scale) propel by itself and by supporting the propeller shaft elastically, and then effects of the number of propeller blades and the form of stern on these values were investigated. Furthermore, taking Weser type stern, its vertical and horizontal surface forces imposed on the part near stern were also measured by a special device, and then a synthetic experiment on propeller exciting forces, including the measurements of thrust,

torque, bearing forces and surface forces was attempted.

The experiments were carried out by making a model ship self-propel along about 200 m straight course in a reservoir, where manipulation, operation of the meters equipped in the ship and recording were all conducted by wireless instructions.

1. Model ship and self-propelling apparatus 1. 1 A model ship and model propellers

Design of a model ship and model propellers were made for anactual ship of LxB xd=220 mx 30.89 mx 1l.67m, Cb=0.80, SHP=25,000HP, N=llO r.p. in and 18.5 K. t under ballast condition. The model ship is Lm xB, x Dm = 5.0 mx

0.7 mx 0.5 m, whose body plan is shown in Fig. I, and general view in Fig. 2. Displacement of ship at the time of experiment was 820 kg, average draught for it 29.9 cm and trin-i 6 cm in stern. In order to prevent hull vibration it is necessary to make rigidity of hull and damping coefficient of vibration as large as possible. The model used here, therefore, was made of steel plate in its deck and bottom over the whole length and its outside shell was of steel plate about L/2 in the mid part. Though the bow, stern and bilge are of wood, the part in the stern are made of duralumin, and by changing this part the forni of stern was altered. (cf.

Fig. 2) As bolts were used for all joints, damping coefficient of the vibration of ship itself became large and it was confirmed that the effect of the vibration of a model ship on measurements is negligible. Hull weight, however, increased because of that, and the draught became larger than 26.6 cm, which is in excess of the corresponding load water draught of the actual ship by about 10 %.

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I I. Main motor

4. Electro-magnetic oscillograph

6. Radio receiver and relay

MEASUREMENT OF PROPELLER FORCES EXCITIIVG HULL VÍBR.4TION BY USE OF SELF-PROPELLED MODEL

Ordinary stern (G-stem)

Weser stern (W-stem) Fig. i Body plan.

Fig. 2. General view of hull structure and arrangement of measuring apparatus.

3

2' 3

4

55

556

7

2. Dynamic Strain meter 3. Dry cell 5. Main battery (100v)

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a--

-I- i -

- -

-Photo. I

In order to investigate the effects of the stern arrangement, tip clearance and screw aperture, the part of stern was changed into the following three kinds. Namely, ordinary stern G1, G.2 and Weser stern W. G7 is an ordinary stern cor-responding to an actual ship. G1 was designed by slightly lengthening G2 under water line and making the screw aperture before the propeller small. (Fig. 6). With a view to investigating the effect of the number of propeller blades on exciting force, four kinds of blades 3, 4, 5 and 6 were used. All of them were aluminum alloy of 170.5 mm in diameter with Troost type section, principal items of which are given in Table I. Ship's speed was measured by a method in which a small propeller type tachometer installed at the position about 20 cm below the surface of water and approximately 2.5 m ahead of stem was led on to the oscillograph to be automatically recorded.

1. 2 Main engine and radio control apparatus

The main engine of the propeller used for a self-propelled model ship is a

DC motor (100V, 1/8 1-IP), and its electric source was supplied by 100V battery, 5 AH equipped in ship. Two sets of radio control apparatuses were used for main instruction and operation, and the former was used for turning

off and on the

switch of main motor and the motor sending the recording paper of electro magnetic oscillograph. For transmitter and receiver, five channel of 27 MC were

Table I Paticulars of model propellers.

Propeller model No. I Il Ill IV

D;ameter ,,,, D 170.5 170.5 170.5 170.5

Number of blades Z 3 4 5 6

Pitch ratio (constant pitch) p 0.728 0.690 0.670 0.648

Developed area ratio a 0.44 0.56 0.66 0.72

Blade thickness ratio 0.05 0.05 0.05 0.05

Boss ratio 0.20 0.20 0.20 0.20

Angle of rake 10' 10' l0 IO'

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MEASUREMENT OF PROPELLER FORCES EXCITING HULL

VIBRATION BY USE OF SELF-PROPELLED MODEL 5

used. They are composed of multiplex control method and ratching-relay circuit. Each sign is therefore independent and can be sent at all times. And for operation pulse width modulation method of 40 MC was adopted.

2. Measuring apparattis of exciting force and method of measurement

2. 1 Thrust and torque

The measuring apparatus of thrust and torque are shown in Fig. 4, (a), (b) and in Photograph 3. In the case of Fig. 4 (b), the thrust imposed on the main shaft is conveyed to the thrust measuring element through the 0.8 inm piano chords from thrust bearing and the force is measured by a strain gauge.

It was to

convey only the thrust from the main shaft and to prevent the force parpendiculer to it, that 0.8mmç piano chorde were used in Fig. 4 (b). In measuring torque, torque-meter with a strain guage was used.

Fig. 3. Screw aperture of model ship (in % of Diameter of propeller)

Stern Experiments Clearance 3 Blade 4 Blade 5 Blade 6 Blade

a 9.7 9.9 12.4 A,C b 13.8 c 8.4 150 9.9 13.9 8.8 s 2.6 2.4 2.4 G1 a 7.1 8.5 9.8 B h c 16.4 8.5 16.4 16.4 0.0 9.0 s 2.5 2.3 2.3 a 11.2 10.2 12.4 11.5 G2 D,E b c 17.8 14.1 18.8 18.4 14.1 14.1 19.5 14.2 i s 3.1 2.5 2.4 1.6 a 11.1 11.1 14.4 12.7 W

F,H,J

b_c s 15.5 10.0 15.9 13.8 9.3 8.1 14.7 8.0

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2

6

(o) Shaft Systemr

(b) Shaft SystemE

Photo. 2

2. 2 Bearing forces

The measuring apparatus of vertical and horizontal forces are shown in Fig. 4 (b). in order to measure vertical and horizontal forces and moments

z

'z

7

1. Rubber packing 8. Bearing force measuring element (vertical)

2. Thrust free bearing 9. Bearing torce measuring element (horizontal)

3. Torque meter lo. Thrust bearing

4. Reduction gear il. Rubber coupling

5. Thrust bearing 12. Cross hinge

6. Tachometer 13. Piano wire (0.8 mm)

7. Thrust measuring element

6 T. KUMAI et al.

Fig. 4 (a). Measuring apparatus for thrust and torque used on experiments (G-A, B). (b). Measuring apparatus for vibratory forces excited by propeller.

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MEASUREMENT OF PROPELLER FORCES EXCITING HULL VIBRATION BY USE OF SELF-PROPELLED MODEL

imposed oil propeller, the propeller shaft was hung at two position (at thrust-free bearing). Measuring the vertical and horizontal reactions at

these points R11, R111, R1, and Rn, the force P and moment M on pro-peller boss were calculated by the following equation. (Fig. 5)

P1_'c,{Ri(l+C) R2}

M=/1R-12(l ±C)R2

provided that C, C' are the correction factors _{for rubber coupling and rubber} packing, which is smaller in value than 1.

2. 3 Surface forces and surface pressure

The measuring apparatus of surface forces on the Weser typestern is shown

in Fig. 6. Calibration of these was executed for F,, by imposing horizontal point-load on the position on the water line _{0.7 R upward from the main shaft and} 5 mm from the trailing edge and for F1 _{by imposing vertical point-load on the} central line right above the propeller tip, while for F, the same process was followed by imposing horizontal point-load at the position on the water line

passing 0.7 R, similarly as in the case of F,1, and the 5 mm from the front edge. The arrangement of the pressure gauge for measuring surface pressure is shown in Fig. 6. The diaphrtgm is mide of steel, 15mm in diameter and 0.04mm in thickness.

26'

-26

Fig. 5. _{Moments and forces which act on} propeller shaft.

I,

Fs Fv FM

Fig. 6 _{Position and apparatus of measuring surface force and surface pressure.}

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8 T. KU MAI et al. 2. 4 Recording apparatus

For recording the forces or the pressure, a portable electro-magnetic oscillo-graph of six elements was used.

3. Method and sort of experimenis

Normal measurement was made when a model ship has reached a condition of steady straight course sailing 80-.-100m after its starting (Photo. 2). lt was

turned at about 5 6 helm angle after it passed the afore-said measuring point, and then stopping of main engine and reversion test were conducted by lowering speed on its return. On low speed, astern test was done immediately after stopping the ship. The measurement of thrust, torque, bearing force, surface pressl.ire and

G1, G2: Ordinary stern

W : Weser stern

T Thrust

Q : Torque

Pp: Port side pressure

P: Starboard side pressure n: r.p.s. of propeller

Photo. 3.

Table 2 The sort of experiments and measurement.

V,: Speed of model ship

R11, RIr: Vertical bearing reaction RI,!, R211: Horizontal bearing reaction Fi,: Horizontal surface force at stern F1: Vertical surface force at stern

F,: Horizontal surface force at rudder stock

Shaft Stern Measurement Propeller

T Q Pp

P, r, V, R11 R111R21 R21, F,, F1' F, A

000000

_3.4.5.B1 G1 _B

000000

G1 C

0 000000

D

000000

I G2 _E

₀

0 0 0 0 0 0

3.4.5.6. Bl II F

00

I

000

W H

0000b00

J

P00000

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others were made seven times; at starting (slip 100%), normal sailing, turning, low speed sailing, stopping of main engine, reversion of propeller arid further at sailing

astern. In the above experiments, the straight course of reservoir was about 200 m, water depth about 3.5 m near the normal measuring point and about 2m in average through the whole course.

Though the present paper deals with only the result of measurement at normal sailing, it corresponds to an actual ship with the speed of about 17 kt.

As mentioned before, since the draft was considerably larger than the value

corresponding to an actual ship and no frictional correction was done, the number of revolution of main engine was increased about 15%, being n= 14 r. p. s. The

zero base was recorded before and after sailing.

The variety of experiments are as shown in Table 2, where thrust, torque and surface pressure are measured for the propelles with 3, 4 and 5 blades with respect to G1 type stern using shaft system I at first. Incidentally, with this G1

type stern, the effects of tip clearance and screw aperture were investigated by putting rings of appropriate thickness before propeller boss and changing the position of propeller into two kinds of A and B. In the next place, measurement of bearing force, surface pressure and surface force beside thrust and torque was made using the shaft system II, but in this case 3-, 4-, 5- and 6-bladed propellers

were used. Tip clearance and screw aperture are shown enbioc in the supplementary table of Fig. 3.

4. Results of experiment

4. 1 Expression of results

Let Mv and Mii vertical and horizontal components of the moment acting on the propeller boss respectively. In the present section, the value divided by M0= T0 x 0.7R was used in order to express these values in non dimension. Here

T0 is average thrust and R the radius of propeller. _{Then putting P, P} vertical

and horizontal forces acting on the center of propeller disk, they were expressed with the ratio to the value of Po=O°R provided that Qo is average torque. M, P can be evaluated from the values of R1, R20 R111, R211 measured as shown in Fig. 5, and here these variational parts are expressed with 4M, 4F, adopting their double amplitude.

In the

result of measurement, the first harmonic (blade frequency) and 2nd harmonic are all evaluated by harmonic analyser, and the harmonics higher than the 2nd are omitted. In the measurements of bearing force and surface force, though more or less different, average values of number of shaft revolution n, ships velocity y5, thrust T0 and torque Qo were n=14.0 r. p. s.

v,= 1.30 rn/sec., T0=3.6kg, Qo=7.3kg-cm respectively. Assuming as wake coefficient

w»0.4 from the result of self-propelled model experiment of an allied ship, we

v5(1w)

have advance coefficient J= -0.32.

nd

4. 2 Variation of thrust and torque

In Fig. 7 the amount of variation of thrust is give n, which shows that, in

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lo AT,,

/T

z 20 60 40 20 o 4 5

No of 5/cides

Fig. 8. Comparison between experiment and calculation of thrust variation.

o-- ist harmonic -.- 2ndnarmoruc T. KU MAI et al. 60 40 20

H-62

-. , - __--.--_____ 0 0-'---

0-3 4 5 6 3 4 5 6 3 4 5 6 No of Blades

Fig. 7. The effect of blade number on thrust variation.

than that in five bladed propellers, what over type the stern may be. Also with the 2nd harmonic, a tendency reverse to it is shown.

And in the case of W type stem in the present experiment, the amount of variation is generally seen to be smaller than G type stern through all the blades.

Thrust variation obtained by van Manen and Wereldsma's experiment [3] and calculated values by one of the authors are in good coincidence with our results as shown in Fig. 8.

As for the variation of torque, no accurate amount of change could be

evaluated in case of shaft system II because of the rubber coupling equipped toit.

60 40 20 60 40

HW

IGe

0 A, ist harmonic __ B Ist harmonic 0-3 4 5 6 No of Blades

Fig. 9. The effect of

blade number on torque variation. Measured Value in this experiments O _{G2 -} _Stern Weser Stern Manens experiments Conventional Stern aMariner Stern Kumai 's ca/culatan XOrdinaly Stern %Weser Stern

/T

z /0

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40 M 7M., z 20 60

Fig. 9 shows variation of each torque when the position of propeller was shifted back and forth on G type stern, using system T. In this case, the effect of the

number of propeller blades shows no definite tendency as seen in the variation of

thrust.

4. 3 Bearing force

The difference in the values of

and the effects of the form of stern on those values are as shown in Figs. 10, 11, 12 and 13. Among those values the one of the ist harmonic or blade frequency shows as a whole gradual decrease with the increase of the number of blades,

LZ-G

- O/st harmonic ..2nd harmonic 0-3 4 5 6 -..No of B/odes 4M

4Mfl 4P

4F1,

and for each blade

M0' M' P0

P0

Fig. IO. The effect of blade number on 4Mr/Mo.

3 4 5 6 3 4 5 6 3 4 5 6

No of B/odes

Fig. Il. The effect of blade number on 4M'/Mo.

60 40 20

17-G2

60 40 20 0

H-W

3 5 6 3 4 5

ll-G

0Ist harmonic -*2nd harmOnic Q-60 40 20 17-G2 60 40 20 Q

H-W

60 /M0 20

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12 60 40 20 'Po y. 20 0-- Ist harmonic _._2nd harmon/C 40 -0- 0-3 4 5 6 3 4 No of 8/odes

Fig. 12. The effect of blade number on 4P-/Po.

\ o--is? harmonic harmonic 40 60 20 3 4 5 6 3 No of 8/odes

Fig. 13. The effect of

whereas the propeller with odd number the one with even number of blades in Manen and Wereldsma's experiment [3]

[6] show nearly the same tendency. 4. 4 Surface pressure and surface force

T. KUMAE et al. 17-G5 60 40 20 blade number on 4PB/F0.

17-W

0-3 4 5

H-W

6 60

I1-Gz

60 40 40 20 20 s.. 0-

0'

Surface pressure was measured by choosing representative positions (cf. Fig. 6) on both boards. Evaluating maximum amplitude of the variation of pressure on both boards separately and comparing it for the number of propeller blade, the result was shown in Fig. 14. When the number of blades increases in of blades shows the tendency to surpass its value. The results obtained in van

and the calculation by one of the authors

/00

60

_H-G'

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E

5

3

MEASUREMENT OF PROPELLER FORCES EXCITING HULL VIBRATION BY USE OF SELF-PROPELLED MODEL

0'

3 4 5 6

No. of Blades

Fig. 14. The effect of blade number on pressure variation.

case screw aperture b/ D is nearly constant, surface pressure decreases. This is

the same with the result obtained by K. H. Pohl [5]. The W type stern of Fig. 14 is larger in pressure change than the G2 type stern, which is presumed mainly due

to the difference in screw aperture. In the present experiment, the propeller turns clockwise, but in either case of Figs. 14, the pressure change of starboard side is larger than that of port side.

Fig. 15 is the result of pressure measurement made by changing ship's speed, but for the change of ship's speed as much as shown in the figure, the increase of surface pressure attending to the increase of ships speed is slight. With respect

L 41- --' 40 30 20

lo

3 4 5 6 s

--/

s-o . 0 /28

/38

1.48 3 4 5 6 Vs "3's -No of Bades

Fig. 15. The effect of ship speed Fig. 16. The effect of blade

on pressure, number on surface

force variation. 13 G, - A 3B/adS -.. ,. -5 P S P S P 5

-.---G-3

o--4

-.0--4

--X.-W' - Stern Proj.Area '-O- Fi 26.0 cm'

-'--

Fv 252 --4k-- Fs /2.5 6 q _{W - Stern} Nao fBI 5 ₃ 0,/55 4 0.159 5 0/38 6 0/47 3 2 0 70 60 50

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14 T. KUMA1 et al.

to the W type stern, the surface forces FN, F1 on a part of stern and the force F8 on the rudder stock were measured. _{The result shows decrease in value with the} increase of the blade number similarly with the surface pressure, _{as shown in}

Fig. 16. _{As it is also plain in the figure, the area subject to pressure} _is _almost

equal, but F11 is considerably larger than F1-.

Conchision

In order to detect the effects of the difference in the number of blade and the form of stern on the variation of bearing force, surface force and thrust, and torque as propeller exciting forces of a single screw ship, a synthetic experimental measurements were made using a self-propelled model ship. _{Though analysis on} a part of the experiments is still kept up, the results of the present study will be summarized as follows:

The variation of thrust is larger in case of blades in even number than in

case of those in odd number. Also in case of W type stern, the amount of change is smaller than in case of G type stern.

Bearing force has a tendency to become smaller the more the number of

propeller blades increases, and reversely to the change of thrust, it is inclined to become large in case of propeller bladed in odd number and small in case of propeller blades in even number.

Surface force and surface pressure decrease with the increase in the number of blades. With the propeller of clockwise revolution, the pressure variation is larger on the starboard side than on the port side.

Also in other experiments lately published, nearly the same tendency has been obtained partly. Though the present experiment deals with propeller exciting forces, further studies are desired to be forwarded in the future on the relation

between wake distribution and bearing force, measurement of the distribution of the pressure on the surface of shell plate and rudder, effect of mutual position of

rudder and propeller as well as the measurement of all the exciting forces including bearing and surface forces.

Acknowledgement

These experiments were carried out during last one year. The authors wish to acknowledge the assistance rendered in this research through a grant from the Research Division of the Ministry of Education in Japan and Mitsui Tamano Shipbuilding and Engineering Works and are also grateful to the Authorities of Kotake Town, Kurate Gun, Fukuoka Prefecture for permitting the use of the

reservoir.

We are especially indebted to Mr. S. Sano for his extraordinary support and our thanks are also due to Prof. Kurihara, the head of Institute for Applied Mechanics of Kyushu University.

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References

[I] Lewis, F. M. and Tachmindji, A. J: "Propeller Force Exciting 1-Iufl Vibration"

S. N. A. M. E. 1954.

Taniguchi, K.: "Measurement of propeller exciting forces by self-propelled model" Bulletin of Western Society of Naval Architecture in Japan No. 12, 1956.

van Manen, J. D. and wereldsma, R.: "Propeller Excited Vibratory Forces in the Shaft of a Single Screw Tanker" I. S. P. Vol. 7, No. 73, 1960.

Taniguchi, K.: "Pressure variation near Propellers" Bulletin of Western Society of Naval Architecture in Japan No. 16, 1958.

Pohl, K. H.:" Die durch eine Schiffschraube auf benachbarten Platten erzeugten Periodischen Hydrodynamischen Drücke." Schiffstechnik Bd. 7, Heft 35, 1960. Kumai, T.: To be read before the meeting of Western Society of Naval Architecture in Japan on Oct. 1961.